Modulation of the Northern Hemisphere Midlatitude Flow and Extreme Events By the Madden-Julian Oscillation

Recent work on teleconnections between the Madden-Julian oscillation (MJO) and northern Hemisphere midlatitude geopotential height anomalies, blocking, and atmospheric rivers (ARs) are discussed. It is first demonstrated using reanalysis fields and a linear baroclinic model that MJO teleconnections to higher latitudes are more robust during certain MJO phases due to the spatial configuration of MJO heating anomalies relative to the North Pacific jet. This robustness is also reflected in excellent ensemble agreement in prediction of North Pacific geopotential height anomalies in a leading numerical weather prediction model at 3-week lead times for certain MJO phases. It is demonstrated that climate and weather forecasting models can have difficulty simulating the spatial pattern and strength of such teleconnections not only due to poor MJO performance, but also due to biases in the spatial extent of the North Pacific jet that affect the pathway of Rossby wave propagation into high latitudes. The modulation of atmospheric blocking and atmospheric river (AR) activity associated with these MJO teleconnections are discussed.

It is also shown that the nature of the MJO teleconnection to the Northern Hemisphere depends on the phase of the tropical quasi-biennial oscillation (QBO). The QBO phase-dependent modulation of AR activity by the MJO along the west coast of North America area is presented. A statistical prediction scheme for anomalous AR activity using the initial state of the MJO and QBO as the sole predictors is developed. When evaluated over 36 boreal winters, it is found that certain combinations of MJO and QBO phases produce predictive skill for anomalous AR activity up to 5 weeks in advance that exceeds that produced by a state-of-the-art numerical weather prediction model. Finally, recent modeling results suggest that the MJO teleconnection to higher latitudes may weaken in a warmer climate. The implications of these weaker teleconnections for subseasonal prediction of blocking and ARs will be discussed.